Domestic humidifying apparatus is generally in the form of a portable appliance having a casing comprising a water tank for storing a volume of water, and a fan for creating a flow of air through an air duct of the casing. The stored water is conveyed, usually under gravity, to an atomizing device for producing water droplets from the received water. This device may be in the form of a heater or a high frequency vibrating device, such as a transducer. The water droplets enter the flow of air passing through the air duct, resulting in the emission of a mist into the environment. The appliance may include a sensor for detecting the relative humidity of the air in the environment. The sensor outputs a signal indicative of the detected relative humidity to a drive circuit, which controls the transducer to maintain the relative humidity of the air in the environment around a desired level. Typically, the actuation of the transducer is stopped when the detected relative humidity is around 5% higher than the desired level, and is restarted when the detected relative humidity is around 5% lower than the desired level.
It is known to provide an ultraviolet radiation (UV) emitting lamp or other UV generator to sterilize water that is conveyed to the atomizing device. For example, U.S. Pat. No. 5,859,952 describes a humidifier in which the water supplied from a tank is conveyed through a sterilizing chamber before being conveyed by a pipe to a chamber containing an ultrasonic atomizer The sterilizing chamber has a UV transparent window beneath which a UV lamp is located to irradiate water as it passes through the sterilizing chamber. U.S. Pat. No. 7,540,474 describes a humidifier in which the water tank includes a UV transparent tube for conveying water to an outlet of the tank, and a main body upon which the tank is mounted includes a UV lamp which irradiates water as it passes through the tube to the outlet.
WO 2013/132222 describes a humidifier which comprises a body and an annular nozzle detachably mounted on the body. The body comprises a base and a water tank removably mounted on the base. A motor-driven impeller located within the base draws an air flow into the humidifier through air inlets located in the outer casing of the base. A first air passageway located downstream from the impeller conveys a first part of the air flow to an annular first interior passage within the nozzle. The first part of the air flow is emitted from a first air outlet of the nozzle. A second air passageway located downstream from the impeller conveys a second part of the air flow over a water reservoir which receives water from the water tank. Transducers located within the water reservoir atomize water stored in the water reservoir to humidify the second part of the air flow. An outlet duct defined by the water tank conveys the humidified air flow to an annular second interior passage of the nozzle. The humidified air flow is emitted from a second air outlet of the nozzle so that the humidified air flow becomes entrained within the air emitted from the first air outlet of the nozzle.
The base has a relatively wide cylindrical outer wall, a relatively narrow cylindrical inner wall located above and co-axial with the outer wall, and a recessed annular wall which extends between the inner wall and the outer wall. These walls of the base define the water reservoir, and so the water reservoir is exposed when the water tank is removed from the base. The water reservoir includes a UV transparent tube housing a UV lamp for irradiating water stored in the water reservoir, and baffle plates for guiding water entering the water reservoir from the water tank over the tube so that it is irradiated by the UV lamp before being atomized by the transducers. The water tank is annular in shape, and is mounted by the user on the annular wall of the base so as to surround the inner wall of the base. The base includes a proximity sensor for detecting that the water tank has been mounted on the base. A drive circuit deactivates the motor, the UV lamp and the transducers in response to signal received from the proximity sensor indicating that the water tank has been removed from the base.
In order for a water tank to supply water to a humidifier it must be provided with a cap assembly which permits the flow of air into the water tank at the same time as permitting a flow of water out of the water tank. Air entering the water tank does so in the form of air bubbles, and the size of the bubbles entering the water tank is determined by the size of the inlets on the tank cap. A known problem with existing water tanks is that in order to permit an adequate flow of air into the water tank they have relatively large sized inlets, which in turn allows relatively large air bubbles to enter the water tank. These large air bubbles create a glugging noise which can be unpleasant for users. In order to reduce the size of the air bubbles entering the water tank, and thus reduce the glugging noise, it would be desirable to reduce the size of the inlets on the tank cap. However, with conventional tank cap designs there is a limit to how small the inlet can be before hydrostatic lock occurs and water is unable to flow out of the water tank.
JP 4726760 B2 describes a tank cap assembly for a humidifier having a movable shaft with a valve at one end disposed on a central portion axially movably against a biasing spring. The tank cap assembly has an inner cylindrical wall mounted on a peripheral edge of a water outflow port and outer cylindrical wall connected with a horizontal partitioning wall. The outer cylindrical wall is longer than the inner cylindrical wall in the direction in which the water flows out of the water tank, and an air inlet is provided on the outer cylindrical wall, such that external air is allowed to flow into the water tank through the air inlet when a water level of a water receiving portion becomes lower than an end face of the inner cylindrical wall.